Acute hypoxia causes a selective release of dopamine from glomus cells without altering the norepinephrine stories in carotid body. A similar pattern of changes in catecholamine content is elicited by the injection of muscarinic receptor agonists. Methylatropine prevents the release of dopamine elicited by methocholine and by acute hypoxia. These findings suggest that a cholinergic muscarinic receptor may mediate dopamine release. In contrast, long lasting hypoxia increased dopamine and norepinephrine content. This response appears to involve induction of tyrosine hydroxylase and hypertrophy and for hyperplasia of glomus cells.